U.S. patent application number 09/769517 was filed with the patent office on 2001-07-26 for augular position measuring device.
Invention is credited to Aoki, Tetsuya, Fukitsuke, Takuya, Hamaoka, Takashi, Kono, Yoshiyuki, Kubota, Takamitsu.
Application Number | 20010009366 09/769517 |
Document ID | / |
Family ID | 27342187 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009366 |
Kind Code |
A1 |
Kono, Yoshiyuki ; et
al. |
July 26, 2001 |
Augular position measuring device
Abstract
A compact and high-accuracy angular position measuring device is
provided which has magnets installed in a rotor core and a magnetic
sensor installed in a stator core. The magnetic sensor produces an
output indicative of an angular position of the rotor core as a
function of a change in density of magnetic flux produced by the
magnets. The magnets are so arranged in the rotor core that the
same poles are opposed magnetically to produce a repellent force in
magnetic fields of the magnets, thereby causing the magnetic flux
to go to the magnetic sensor through the rotor core. This
eliminates the need for an air gap between the stator core and the
poles of the magnets which is formed in a conventional device, thus
allowing the device to be reduced in size and an error in output of
the device to be decreased.
Inventors: |
Kono, Yoshiyuki; (Obu-shi,
JP) ; Hamaoka, Takashi; (Kariya-shi, JP) ;
Kubota, Takamitsu; (Kariya-shi, JP) ; Fukitsuke,
Takuya; (Tokai-shi, JP) ; Aoki, Tetsuya;
(Toyoake-shi, JP) |
Correspondence
Address: |
Pillsbury Madison & Sutro LLP
Intellectual Property Group
Ninth Floor, East Tower
1100 New York Avenue, N.W.
Washington
DC
20005-3918
US
|
Family ID: |
27342187 |
Appl. No.: |
09/769517 |
Filed: |
January 26, 2001 |
Current U.S.
Class: |
324/207.2 ;
324/207.25 |
Current CPC
Class: |
G01D 5/145 20130101 |
Class at
Publication: |
324/207.2 ;
324/207.25 |
International
Class: |
G01B 007/30; G01B
007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2000 |
JP |
2000-21822 |
Feb 29, 2000 |
JP |
2000-53927 |
Apr 19, 2000 |
JP |
2000-117703 |
Claims
What is claimed is:
1. An angular position measuring device comprising: a stationary
member; a rotatable member rotatable following rotation of an
object to be measured in angular position; a plurality of magnets
installed in one of said stationary member and said rotatable
member so that the same poles are opposed magnetically to produce a
repellent force in magnetic fields of the magnets; and a sensor
element installed in the other of said stationary member and said
rotatable member, said sensor element being responsive to a change
in density of magnetic flux produced by said magnets to provide an
output as a function of an angular position of the object.
2. An angular position measuring device as set forth in claim 1,
wherein each of said magnets is made of one of a plate and a
cylindrical member whose ends are magnetized.
3. An angular position measuring device as set forth in claim 1,
wherein said rotatable member is made of a hollow cylindrical yoke
having installed therein said magnets, and said stationary member
is made of a stator core having installed therein said sensor
element and disposed inside the cylindrical yoke, and further
comprising a sensor gap formed in the stator core within which said
sensor element is disposed.
4. An angular position measuring device as set forth in claim 3,
wherein the cylindrical yoke has air cavities formed in an inner
surface thereof which open to said magnets for avoiding a short of
the magnetic flux between each pole of the magnets and the stator
core.
5. An angular position measuring device as set forth in claim 1,
wherein said magnets are so arranged as to define two magnetic
paths along which the magnetic fluxes produced by said magnets
pass, the magnetic paths extending symmetrically through said
stationary member and said rotatable member.
6. An angular position measuring device as set forth in claim 3,
wherein the stator core is made of three or more parts which are so
fabricated as to define air gaps one of which is the sensor gap
within which said sensor element is disposed.
7. An angular position measuring device as set forth in claim 6,
wherein the air gaps extend radially in the stator core at a
regular angular interval, and wherein said magnets are arranged at
an angular interval identical with the angular interval of the air
gaps.
8. An angular position measuring device as set forth in claim 6,
wherein the stator core is circular in cross section, and wherein
the one of the air gaps employed as the sensor gap is longer than a
radius of the stator core.
9. An angular position measuring device as set forth in claim 8,
wherein the one of the air gaps as employed as the sensor gap is
longer than the other air gaps.
10. An angular position measuring device as set forth in claim 3,
wherein the stator core has formed in at least one of ends of the
sensor gap a greater air cavity which serves to concentrate the
magnetic flux at the sensor gap.
11. An angular position measuring device as set forth in claim 1,
further comprising an air gap defined between an inside of said
rotatable member and an outside of said stationary member, said air
gap being so oriented geometrically that an interval between the
inside of said rotatable member and the outside of said stationary
member varies in a direction of rotation of said rotatable
member.
12. An angular position measuring device as set forth in claim 11,
wherein the interval between the inside of said rotatable member
and the outside of said stationary member is maximized at each of
the poles of said magnets.
13. An angular position measuring device as set forth in claim 12,
wherein said rotatable member is made of a hollow member defining
therein an oval chamber in which said stationary member made of a
cylindrical member is disposed.
14. An angular position measuring device as set forth in claim 3,
further comprising an air gap defined between an inside of said
cylindrical yoke and an outside of said stator core, said air gap
being defined by an interval between the inside of said cylindrical
yoke and the outside of said stator core which varies in a
circumferential direction of the inside of said cylindrical
yoke.
15. An angular position measuring device as set forth in claim 14,
wherein the interval between the inside of said cylindrical yoke
and the outside of said stator core is maximized at each of the
poles of said magnets.
16. An angular position measuring device as set forth in claim 15,
wherein said cylindrical yoke defines therein an oval chamber in
which said stator core is disposed.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field of the Invention
[0002] The present invention relates generally to an improved
structure of a device for measuring an angular position of an
object using a magnetic detector and magnets, and more particularly
to a compact and high-accuracy angular position measuring
device.
[0003] 2. Background Art
[0004] U.S. Pat. No. 5,861,745 (Japanese Patent First Publication
No. 2920179, PCT:WO98/080601) discloses an angular position
measuring device using a magnetic detector such as a Hall element
and magnets.
[0005] FIG. 19 shows one example of conventional angular position
measuring devices designed to measure an opened position of a
throttle valve of an internal combustion engine. The device
includes a cylindrical rotor core (i.e., a yoke) 11 rotating along
with the throttle valve (not shown) and a stator core 12 disposed
coaxially within the rotor core 11. Disposed between the rotor core
11 and the stator core 12 are two arc-shaped magnets 13 which are
diametrically opposed to each other. Each of the magnets 13 is so
magnetized that all lines of magnetic force are oriented in a
radius direction of the magnet 13. A magnetic gap 14 is formed in
the stator core 12 which has a constant width and extends through
the center of the stator core 12 in a diameter direction. A
magnetic detector such as a Hall IC is disposed at the center of
the magnetic gap 14.
[0006] The density of a magnetic flux through the magnetic gap 14
in the stator core 12 changes as a function of an angular position
of the rotor core 11. The magnetic detector 15 produces an output
as a function of the magnetic flux density. Specifically, the
angular position of the rotor core 11, or the opened position of
the throttle valve is determined using the output of the magnetic
detector 15.
[0007] The arc-shaped magnets 13 are, as described above,
magnetized radially. Uniformly magnetizing the magnets 13 requires
decreasing the magnetic flux density in an outer peripheral portion
of the magnets 13, while increasing the magnetic flux density in an
inner peripheral portion of the magnets 13. Such magnets are,
however, difficult to produce and may have a great variation in
quality. The variation in quality will lead to an error in an
output of the magnetic detector 15.
[0008] Additionally, the installation of the magnets 13 between the
rotor core 11 and the stator core 12 will result in an increase in
diameter of the rotor core 11, thereby leading to an increase in
overall size of the angular position measuring device.
SUMMARY OF THE INVENTION
[0009] It is therefore a principal object of the invention to avoid
the disadvantages of the prior art.
[0010] It is another object of the invention to provide a compact
angular position measuring device capable of determining an angular
position of a rotary object with high accuracy.
[0011] According to one aspect of the invention, there is provided
an angular position measuring device which comprises: (a) a
stationary member; (b) a rotatable member rotatable following
rotation of an object to be measured in angular position; (c) a
plurality of magnets installed in one of the stationary member and
the rotatable member so that the same poles are opposed
magnetically to produce a repellent force in magnetic fields of the
magnets; and (d) a sensor element installed in the other of the
stationary member and the rotatable member, the sensor element
being responsive to a change in density of magnetic flux produced
by the magnets to provide an output as a function of an angular
position of the object.
[0012] In the preferred mode of the invention, each of the magnets
is made of one of a plate and a cylindrical member whose ends are
magnetized.
[0013] The rotatable member is made of a hollow cylindrical yoke
having installed therein the magnets. The stationary member is made
of a stator core having installed therein the sensor element and
disposed inside the cylindrical yoke. A sensor gap is formed in the
stator core within which the sensor element is disposed.
[0014] The cylindrical yoke may have air cavities formed in an
inner surface thereof which open to the magnets for avoiding a
short of the magnetic flux between each pole of the magnets and the
stator core.
[0015] The magnets may be so arranged as to define two magnetic
paths along which the magnetic fluxes produced by the magnets pass.
The magnetic paths extend symmetrically through the stationary
member and the rotatable member.
[0016] The stator core is made of three or more parts which are so
fabricated as to define air gaps one of which is the sensor gap
within which the sensor element is disposed.
[0017] The air gaps extend radially in the stator core at a regular
angular interval. The magnets are arranged at an angular interval
identical with the angular interval of the air gaps.
[0018] The stator core may be circular in cross section. The one of
the air gaps employed as the sensor gap is longer than a radius of
the stator core.
[0019] The one of the air gaps as employed as the sensor gap is
longer than the other air gaps.
[0020] The stator core may have formed in at least one of ends of
the sensor gap a greater air cavity which serves to concentrate the
magnetic flux at the sensor gap.
[0021] An air gap may be defined between the inside of the
cylindrical yoke and the outside of the stator core. The air gap is
defined by an interval between the inside of the cylindrical yoke
and the outside of the stator core which varies in a
circumferential direction of the inside of the cylindrical
yoke.
[0022] The interval may be maximized at each of the poles of said
magnets.
[0023] The cylindrical yoke defines therein an oval chamber in
which the stator core is disposed.
BRIEF DESPCRIPTION OF THE DRAWINGS
[0024] The present invention will be understood more fully from the
detailed description given hereinbelow and from the accompanying
drawings of the preferred embodiments of the invention, which,
however, should not be taken to limit the invention to the specific
embodiments but are for the purpose of explanation and
understanding only.
[0025] In the drawings:
[0026] FIG. 1 is a sectional view which shows an angular position
measuring device according to the first embodiment of the
invention;
[0027] FIG. 2 is a vertical sectional view which shows the angular
position measuring device of FIG. 1;
[0028] FIG. 3 is a graph which shows a relation between a
rotational angle of a rotor core and the density of magnetic flux
passing through a Hall IC;
[0029] FIG. 4 is a sectional view which shows an angular position
measuring device according to the second embodiment of the
invention;
[0030] FIG. 5 is a vertical sectional view which shows an angular
position measuring according to the third embodiment of the
invention;
[0031] FIG. 6 is a sectional view which shows an angular position
measuring device according to fourth embodiment of the
invention;
[0032] FIG. 7 is a sectional view which shows an angular position
measuring device according to the fifth embodiment of the
invention;
[0033] FIG. 8 is a sectional view which shows an angular position
measuring device according to the sixth embodiment of the
invention;
[0034] FIG. 9 is a sectional view which shows an angular position
measuring device according to the seventh embodiment of the
invention;
[0035] FIG. 10 is a graph which shows a relation between a
rotational angle of a rotor core and the density of magnetic flux
passing through a Hall IC in the seventh embodiment;
[0036] FIG. 11 is a sectional view which shows an angular position
measuring device according to the eighth embodiment of the
invention;
[0037] FIG. 12 is a graph which shows a relation between a
rotational angle of a rotor core and the density of magnetic flux
passing through a Hall IC in the eighth embodiment;
[0038] FIG. 13 is a sectional view which shows an angular position
measuring device according to the ninth embodiment of the
invention;
[0039] FIGS. 14 to 16 are sectional views which show modifications
of the angular position measuring device shown in FIG. 13;
[0040] FIG. 17 is a sectional view which shows an angular position
measuring device according to the tenth embodiment of the
invention;
[0041] FIG. 18 is a sectional view which shows a modification of
the angular position measuring device shown in FIG. 17; and
[0042] FIG. 19 is a sectional view which shows a conventional
angular position measuring device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Referring to the drawings, wherein like reference numbers
refer to like parts in several views, particularly to FIGS. 1 and
2, there is shown an angular position measuring device according to
the invention.
[0044] The angular position measuring device generally includes a
device housing 21, a cup-shaped rotor core (i.e., a yoke) 24, and a
cylindrical stator core 25. The device housing 21 has disposed
therein a bearing 23 coupled to a rotary shaft 22 of, for example,
a throttle valve of an internal combustion engine (not shown) to be
measured in a rotational angle or angular position. The rotor core
24 is attached to an end of the rotary shaft 22 by staking. The
stator core 25 is disposed in the rotor core 24 coaxially
therewith. The rotor core 24 and the stator core 25 are each made
of a magnetic material such as iron.
[0045] The rotor core 24, as clearly shown in FIG. 1, has formed
therein diametrically opposed recesses 26 within which magnets 27
are fitted using adhesive, respectively. Each of the magnets 27 is
made of a cylindrical or plate member which has two opposed ends
magnetized to have North and South poles. The magnets 27 are so
arranged that the same poles thereof are opposed in a
circumferential direction to produce the repellent force in
magnetic fields of the magnets 27. Semi-circular small air gaps 50
which are diametrically opposed to each other are formed between an
inner surface of the rotor core 24 and an outer surface of the
stator core 25 except vicinities of the magnets 27 so that the
magnetic flux emerging from the North pole of each of the magnets
27 may pass through the stator core 25 from the rotor core 24 and
return back to the South pole of the magnets 27 through the rotor
core 24. The rotor core 24 has air cavities 28 formed in the
vicinity of the magnets 27 for avoiding a short of the magnetic
flux between each pole of the magnets 27 and the stator core 25,
thereby avoiding a reduction in density of the magnetic flux
through the stator core 25 to ensure the measurement accuracy of
the angular position measuring device.
[0046] A constant sensor gap 29 is formed in the stator core 25
which passes through the center thereof in a diameter direction.
The sensor gap 29 serves to form therein a parallel magnetic field.
The stator core 25 is, as can be seen from FIG. 2, made up of two
semi-cylindrical members which are held at a given interval away
from each other by a resinous spacer 30, thereby defining the
sensor gap 29. Two Hall ICs 31 are arrayed adjacent to each other
within the sensor gap 29. Each of the Hall ICs 31 has installed
therein a magnetic sensor and an amplifier and works to produce a
voltage signal as a function of the density of a magnetic flux
passing therethrough. Each of the Hall ICs 31 may have functions of
output gain adjustment, offset adjustment, electrically trimming a
temperature characteristic-correcting program using an external
device, and self-diagnosing a breakage and short of an electric
circuit.
[0047] The Hall ICs 31 are positioned by the spacer 30 and have
terminals which pass through the spacer 30 and are welded to
connector pins 32. The connector pin 32, the stator core 24, and
the spacer 30 are installed in a connector housing 33 which is
molded from a resinous material. The connector housing 33 has
formed in a left surface, as viewed in FIG. 2, an annular groove 34
into which the end of the device housing 21 is press-fitted and
bonded, thereby holding a coaxial relation between the rotor core
24 and the stator core 25.
[0048] The two magnets 27 are, as described above, so arranged in
diametrically opposed portions of the rotor core 24 as to produce
the repellent force in the magnetic fields thereof. The magnetic
flux emerging from the North pole of each of the magnets 27, thus,
goes to the stator core 25 through the rotor core 24 to the sensor
gap 29 (i.e., the Hall ICs 31) and back to the rotor core 24
through the stator core 25 and enters the South pole of the magnet
27. When the rotor core 24 starts to rotate following rotation of
the rotary shaft 22, it will cause the density of magnetic flux
through the sensor gap 29 of the stator core 25 to change, as shown
in FIG. 3, as a function of a rotational angle of the rotor core
24, so that each of the Hall ICs 31 produce a voltage output
proportional to the rotational angle of the rotor core 24. The
determination of the rotational angle or angular position of the
rotor core 24 is made using two voltage outputs from the Hall ICs
31. For example, if a difference between the two voltage outputs
exceeds a given value, it may be concluded that some failure has
occurred in the angular position measuring device.
[0049] The installation of the two magnets 27 in the diametrically
opposed portions of the rotor core 24 in such a manner that the
same poles are opposed to each other in a circumferential direction
of the rotor core 24 eliminates the need for an air gap, like the
one shown in FIG. 19, between the pole surfaces of the magnets 27
and the periphery of the stator core 25, thereby increasing the
degree of freedom of design of the magnets 27 which allows each of
the magnets 27 to be formed by a plate or cylindrical member that
is easy to manufacture and magnetize. This also results in a
decrease in error of outputs of the Hall ICs 31, thus increasing
the accuracy in determining the angular position of the rotary
shaft 22. Further, the arrangement of the magnets 27 in this
embodiment eliminates the need for installation of the magnets 27
on an inner peripheral surface of the rotor core 24, thereby
allowing the rotor core 24 to be reduced in size in the radius
direction thereof.
[0050] FIG. 4 shows an angular position measuring device according
to the second embodiment of the invention.
[0051] The magnets 27 are so installed in the rotor core 24 that a
circumferential distance between the North poles of the magnets 27
is greater than that between the South poles. Of course, the
circumferential distance between the South poles of the magnets 27
may be greater than that between the North poles. The air cavities
28 serving to avoid a short of the magnetic flux between each pole
of the magnets 27 and the stator core 25 extend longer than in the
first embodiment. Other arrangements are identical with those in
the first embodiment, and explanation thereof in detail will be
omitted here.
[0052] If the paths of the magnetic flux produced by the two
magnets 27 are symmetrical, as shown in FIG. 4, the magnetic flux
density, as shown in FIG. 3, increases and decreases symmetrically
as a function of a rotational angle of the rotor core 24, however,
the invention is not always limited to such a geometrical
relation.
[0053] The above embodiments form each path of the magnetic flux
using one of the magnets 27, however, may employ a plurality of
magnets which are so arrayed that the North pole of one of the
magnets is in contact with the South pole of an adjacent one for
strengthening the magnetic field. Alternatively, three or more
magnets may be so installed in the rotor core 24 at given intervals
that adjacent two of the magnets produce a repellent force. In this
case, the Hall ICs 31 are disposed in an area through which the
magnetic fluxes produced by adjacent two of the magnets pass in
parallel.
[0054] The shape of the magnets 27 is not limited to a cylindrical
or flat one and may be determined in view of an installation place
or ease of manufacture. The magnets 27 may be different in size
from each other.
[0055] FIG. 5 shows an angular position measuring device according
to the third embodiment of the invention. The same reference
numbers as employed in the first embodiment refer to the same
parts, and explanation thereof in detail will be omitted here.
[0056] A rotary lever 41 is molded from a resinous material and has
formed integrally therein the rotor core 24 within which two
magnets 27 are installed. The rotary lever 41 is coupled to an
object to be measured in angular position and has a cavity within
which the stator core 25 is fitted in contact with an inner wall
(i.e., a bearing surface) of the cavity so that the rotary lever 41
may rotate in synchronization with the object. A coil spring 43 is
connected at one end to an inner wall of a cylindrical cover 49 and
at the other end to the rotary lever 41 so that upon release of
torque transmitted from the object, the rotary lever 41 is returned
back to an angular null position.
[0057] A shaft 45 made of a non-magnetic material is fitted in a
recess formed in the center of an end surface of the stator core
25. The shaft passes through a hole 46 formed in the rotary lever
41. A stopper plate 47 is fitted in a groove formed in the head of
the shaft 45 to prevent the rotary lever 45 from being dislodged
from the shaft 45 (i.e., the stator core 25). A spring washer 48 is
disposed between the stopper plate 47 and the rotary lever 41 to
minimize the thrust of the rotary lever 41.
[0058] The connector housing 33 is formed integrally with the cover
49. The cover 49 has disposed therein the rotary lever 41 and the
rotor core 24. The magnets 27 are, like the first embodiment, so
arranged in diametrically opposed portions of the rotor core 24 as
that the magnetic flux emerging from the North pole of each of the
magnets 27 goes to the stator core 25 through the rotor core 24 to
the sensor gap 29 (i.e., the Hall ICs 31) and back to the rotor
core 24 through the stator core 25 and enters the South pole of the
magnet 27. Other arrangements are identical with those in the first
embodiment.
[0059] FIG. 6 shows an angular position measuring device according
to the fourth embodiment of the invention which is different from
the first and second embodiments in that the stator core 25 has
formed therein air cavities 51 that are oval in cross section.
Other arrangements are identical, and explanation thereof in detail
will be omitted here.
[0060] The air cavities 51 are formed in diametrically opposed
peripheral portions of the stator core 25 so that they communicate
with ends of the sensor gap 29, respectively. The formation of the
air cavities 51 causes the magnetic flux produced by each of the
magnets 27 to concentrate at the center of the stator core 25, that
is, the Hall ICs 31 installed in the sensor gap 29, thus resulting
in an increase in density of the magnetic flux passing through the
Hall ICs 31. This increase will result in an increase in output of
the Hall ICs 31, thereby allowing an amplification factor of an
output from each of the Hall ICs 31 to be decreased. The decreasing
of the amplification factor will minimize undesirable effects of a
change in temperature of the Hall ICs 31 on outputs of the Hall ICs
31 and also allows the amplifier installed in each of the Hall ICs
31 to be simplified in circuit structure.
[0061] Each of the air cavities 51 communicates with the air
cavities 28 through a slit 60 formed in the periphery of the stator
core 25, thereby providing as wide an outer surface of the stator
core 25 into which the magnetic flux enters as possible. This
causes a greater magnetic flux from the rotor core 24 to enter the
stator core 25, thus increasing the outputs of the Hall ICs 31.
[0062] FIG. 7 shows an angular position measuring device according
to the fifth embodiment of the invention which is different from
the fourth embodiment only in that the air gap 50 is formed to be
constant in width without forming the air cavities 28 in the rotor
core 24. Other arrangements are identical, and explanation thereof
in detail will be omitted here.
[0063] The air cavities 51 which are formed in diametrically
opposed peripheral portions of the stator core 25, like the fourth
embodiment, serve to concentrate the magnetic flux produced by each
of the magnets 27 at the sensor gap 29, thus resulting in an
increase in density of the magnetic flux passing through the Hall
ICs 31 and also work to avoid a short of the magnetic flux between
each pole of the magnets 27 and the stator core 25.
[0064] FIG. 8 shows an angular position measuring device according
to the sixth embodiment of the invention which is different from
the first to fifth embodiments in that a rotor core 52 is made of a
cylindrical member that is oval or elliptical in cross section.
Other arrangements are identical, and explanation thereof in detail
will be omitted here.
[0065] The rotor core 52 has formed in its ends in a longitudinal
direction thereof recesses 53 within which magnets 54 are fitted
using adhesive, respectively. The air gap 50 between the rotor core
52 and the stator core 25 increases in volume as approaching each
of the magnets 54 (i.e., each pole of the magnets 54), thereby
defining a greater air cavity around each of the magnets 54 which
serves, like the air cavities 28, to avoid a short of the magnetic
flux between one of poles of the magnets 54 and the stator core
25.
[0066] The air gap 50 decreases in volume gradually as leaving from
each of the magnets 54, thereby preventing the magnetic flux from
the inner surface of the rotor core 52 to the outer surface of the
stator core 25 from being biased toward each of the magnets 54,
thus resulting in uniformity of the magnetic flux entering the
stator core 25. This improves the linearity of a change in density
of the magnetic flux in the sensor gap 29 with a change in
rotational angle of the rotor core 52.
[0067] FIG. 9 shows an angular position measuring device according
to the seventh embodiment of the invention.
[0068] The angular position measuring devices of the first to sixth
embodiments are so designed that the density of a magnetic flux
passing through the sensor gap 29 increases and decreases in a
cycle of 180.degree. (see FIG. 3) and, thus, have an effective
angular position-measuring range of 180.degree. or less within
which an output of each of the Hall ICs 31 changes linearly. The
angular position measuring device of this embodiment is so designed
as to have a wider angular position-measuring range over
180.degree..
[0069] The stator core 55 is made up of three parts which are
assembled to define three sensor gaps 56 which extend radially from
the center thereof at an angular interval of 120.degree.. The Hall
IC 31 is disposed within one of the sensor gaps 56. Two magnets 27
are installed in the rotor core 24 at an angular interval of
120.degree. which is equal to that of the sensor gaps 56. The rotor
core 24 has two air cavities 28 formed in the vicinity of the
magnets 27 for avoiding a short of the magnetic flux between each
pole of the magnets 27 and the stator core 25. Other arrangements
are identical with those of the first embodiment, and explanation
thereof in detail will be omitted here.
[0070] When the rotor core 24 is in a position as shown in FIG. 9,
the magnetic flux emerging from the North pole of a right one of
the magnets 27 goes to an upper right portion of the stator core 55
through the rotor core 24 to a right one of the sensor gaps 56
(i.e., the Hall IC 31) and back to the rotor core 24 through a
lower right portion of the stator core 55 and enters the South pole
of the right magnet 27. The magnetic flux emerging from the North
pole of a left one of the magnets 27 goes to an upper left portion
of the stator core 55 through the rotor core 24 to a left one of
the sensor gaps 56 and back to the rotor core 24 through a lower
left portion of the stator core 55 and enters the South pole of the
left magnet 27.
[0071] When the rotor core 24 starts to rotate, it will cause the
density of magnetic flux through each of the right and left sensor
gaps 56 of the stator core 55 to decrease, as shown in FIG. 10, as
a function of a rotational angle of the rotor core 24 within a
range of approximately 0.degree. to 230.degree. and then increase
as a function of a rotational angle of the rotor core 24 within a
range of approximately 240.degree. to 350.degree..
[0072] Specifically, the range within which the density of magnetic
flux passing through the Hall IC 31 decreases linearly is
asymmetrical with, that is, wider than the range within which the
density of magnetic flux passing through the Hall IC 31 increases
linearly, thereby enabling the angular position measuring device of
this embodiment to produce an output which changes linearly as a
function of a rotational angle of the rotor core 24 over an angular
range of approximately 220.degree..
[0073] FIG. 11 shows an angular position measuring device according
to the eighth embodiment of the invention which is different from
the seventh embodiment in that the stator core 55 is made up of
four parts which are assembled to form four sensor gaps 56 which
extend radially from the center thereof at an angular interval of
90.degree., and two magnets 27 are installed in the rotor core 24
at an angular interval of 90.degree.. Other arrangements are
identical, and explanation thereof in detail will be omitted
here.
[0074] When the rotor core 24 is in a position as shown in FIG. 11,
the magnetic flux emerging from the North pole of a right one of
the magnets 27 goes to an upper right portion of the stator core 55
through the rotor core 24 to a right one of the sensor gaps 56
within which the Hall IC 31 is installed and back to the rotor core
24 through a lower right portion of the stator core 55 and enters
the South pole of the right magnet 27. The magnetic flux emerging
from the North pole of the lower magnet 27 goes to a lower left
portion of the stator core 55 through the rotor core 24 to the
lower sensor gap 56 and back to the rotor core 24 through a lower
right portion of the stator core 55 and enters the South pole of
the lower magnet 27.
[0075] The angular position measuring device of this embodiment is
capable of producing an output which changes, as shown in FIG. 12,
linearly as a function of a rotational angle of the rotor core 24
over an angular range of approximately 200.degree..
[0076] FIG. 13 shows an angular position measuring device according
to the ninth embodiment of the invention which is a modification of
the one shown in FIG. 9.
[0077] The stator core 55 has three air cavities 57, like the air
cavities 51 shown in FIGS. 6, 7, and 8, which are oval in cross
section and which serve to concentrate the magnetic flux on the
Hall IC 31 installed in one of the sensor gaps 56.
[0078] The air gap 50 between the rotor core 24 and the stator core
55 increases in volume as approaching each of the magnets 27,
thereby defining a greater air cavity around each of the magnets 27
which serves, like the air cavities 28, to avoid a short of the
magnetic flux between one of poles of the magnets 27 and the stator
core 55.
[0079] FIG. 14 shows an angular position measuring device which is
a modification of the one shown in FIG. 11.
[0080] The stator core 55 has four air cavities 57, like the air
cavities 51 shown in FIGS. 6, 7, and 8, which are oval in cross
section and which serve to concentrate the magnetic flux at the
Hall IC 31 installed in one of the sensor gaps 56.
[0081] The air gap 50 between the rotor core 24 and the stator core
55 increases in volume as approaching each of the magnets 27,
thereby defining a greater air cavity around each of the magnets 27
which serves, like the air cavities 28, to avoid a short of the
magnetic flux between one of poles of the magnets 27 and the stator
core 55.
[0082] The air gap 50 decreases in volume gradually as leaving from
each of the magnets 54, thereby preventing the magnetic flux from
the inner surface of the rotor core 52 to the outer surface of the
stator core 25 from being biased toward each of the magnets 54,
thus resulting in uniformity of the magnetic flux entering the
stator core 25. This improves the linearity of a change in density
of the magnetic flux in the sensor gap 29 with a change in
rotational angle of the rotor core 52.
[0083] FIG. 15 shows an angular position measuring device which is
a modification of the one shown in FIG. 13.
[0084] The stator core 55 is formed coaxially with the rotor core
24 so as to form a constant air gap 50 between the stator core 55
and the rotor core 24. Other arrangements are identical with those
in FIG. 13, and explanation thereof in detail will be omitted
here.
[0085] FIG. 16 shows an angular position measuring device which is
a modification of the one shown in FIG. 14.
[0086] The stator core 55 is formed coaxially with the rotor core
24 so as to form a constant air gap 50 between the stator core 55
and the rotor core 24. Other arrangements are identical with those
in FIG. 14, and explanation thereof in detail will be omitted
here.
[0087] While the sensor gaps 56 in the seventh to ninth embodiments
are formed at regular angular intervals, they may alternatively be
arranged at irregular angular intervals depending upon a desired
angular position-measuring range. Further, the angular interval
between the two magnets 27 may be different from that of the air
gaps 56. In this case, the same effects as provided by the seventh
to ninth embodiments are obtained by modifying the location and/or
the shape of the magnetic flux short-avoiding air cavities 28
formed in the rotor core 24 as needed.
[0088] FIG. 17 shows an angular position measuring device according
to the tenth embodiment of the invention.
[0089] In the angular position measuring device of each of the
first to sixth embodiments, the sensor gap 29 extends over a
diameter of the stator core 25 and has a length sufficient to array
the two Hall ICs 31. However, the angular position measuring device
in each of the seventh to ninth embodiments has formed therein more
than two sensor gaps whose length is equal to the radius of the
stator core 25 and may be insufficient to array two Hall ICs if the
stator core 25 is decreased in size for compactness of the device.
In order to avoid this problem, the angular position measuring
device of the tenth embodiment makes a stator core of three or more
parts so as to form at least one air gap longer than the radius of
the stator core.
[0090] Specifically, the stator core 61 is made up of three parts
so as to define two shorter air gaps 64 and one longer air gap 62.
The air gaps 64 are aligned with each other horizontally, as viewed
in the drawing. Upper two of the three parts of the stator core 61
are symmetrical so as to have the air gap 64 pass through the
center of the stator core 61. The air gap 64, thus, has the length
longer than the radius of the stator core which is sufficient to
array two Hall ICs 31.
[0091] Two magnets 27 are so arranged in the rotor core 24 that
when one of the magnets 27 face an end of one of the air gaps 64,
the other magnet 27 face a diametrically opposed end of the other
air gap 64. Cavities like the air cavities 51 as shown in FIGS. 6,
7, and 8 may be formed in the air gaps 64.
[0092] FIG. 18 shows an angular position measuring device which is
a modified form of the one shown in FIG. 17 and different therefrom
only in that two air gaps 64 inclined downward, as viewed in the
drawing, without being aligned with each other. This structure also
provides the same effects as in the above tenth embodiment.
[0093] While the present invention has been disclosed in terms of
the preferred embodiments in order to facilitate better
understanding thereof, it should be appreciated that the invention
can be embodied in various ways without departing from the
principle of the invention. Therefore, the invention should be
understood to include all possible embodiments and modifications to
the shown embodiments witch can be embodied without departing from
the principle of the invention as set forth in the appended claims.
For example, the two Hall ICs 31 may be laid to overlap each other
in parallel to the magnetic flux in the sensor gap 29.
Alternatively, a single Hall IC may be used or three or more Hall
ICs may be arrayed in parallel or perpendicular to the magnetic
flux depending upon the size of the sensor gap 29. Instead of the
Hall ICs 31, magnetoresistive elements may be employed. Further,
the rotor core 24 or 52 in the above embodiments is installed in
the device housing 21 to be rotatable in synchronism with rotation
of the rotary shaft 22, however, it may be secured to the device
housing 21 to be stationary, while the inner core 25, 55, or 61 may
be retained by the connector housing 33 to be rotatable following
rotation of the rotary shaft 22.
* * * * *